Why don’t you use markdown?
| quantity | dimensional formula | 
|---|---|
| period p | L^0 M^0 T^1 | 
| length of string \ell | L^1 M^0 T^0 | 
| quantity  |  dimensional formula  |
|---:|:---|
|  period $p$  |  $L^0 M^0 T^1$  |
|  length of string $\ell$  |  $L^1 M^0 T^0$  |
Why don’t you use markdown?
| quantity | dimensional formula | 
|---|---|
| period p | L^0 M^0 T^1 | 
| length of string \ell | L^1 M^0 T^0 | 
| quantity  |  dimensional formula  |
|---:|:---|
|  period $p$  |  $L^0 M^0 T^1$  |
|  length of string $\ell$  |  $L^1 M^0 T^0$  |